The premise behind the widespread use of androgenic steroids by athletes that these agents enhance protein synthesis and muscle strength is not supported by data. In this regard, the objectives of the proposed studies are to examine whether superphysiological doses of androgenic steroids promote nitrogen retention, protein synthesis and skeletal muscle performance in eugonadal men. It s hypothesized that androgenic steroids promote nitrogen retention and protein synthesis only in hypogonadal men, and that superphysiological doses of androgenic steroids do not further increase nitrogen retention, protein synthesis or muscle strength when confounding variables such as exercise training stimulus and dietary intake are controlled. Four groups of ten healthy, eugonadal men will be treated as follows: Group 1: vehicle, no exercise; Group 2: vehicle, exercise training, Group 3: testosterone enanthate (TE) 600 mg 1M every week, no exercise. Group 4: TE (600 mg/wk) plus exercise training. The following will be studied before and after 10 weeks of treatment: cross-sectional areas of the muscle and subcutaneous tissue of the arm and the thigh by MR scanning; modified nitrogen balance assessed by urinary and fecal nitrogen measurements during a defined nitrogen intake; whole body L-[1-13C] leucine turnover and oxidation; fractional muscle protein synthesis; body composition analysis by H2 18O dilution and hydrostatic weighing; maximal muscle strength by 1RM of a defined weight lifting exercise, and submaximal muscle performance by analysis of integrated EMG: force relationships. In addition total and free testosterone (T), dihydrotestosterone, LH, FSH and SHBG levels will be monitored before, during and after treatment as markers of androgen bioavailability and action. Confounding variables such as age, caloric and protein intake, and the level of exercise training stimulus will be strictly controlled. In addition, ten hypogonadal men will undergo the following studies before and after 10 weeks of TE (100 mg/wk) primarily to demonstrate that replacement doses of androgenic steroids promote nitrogen retention and protein synthesis in hypogonadal men; modified nitrogen balance, whole body L-[1-13C] leucine turnover and oxidation; fractional muscle protein synthesis; cross-sectional areas of the muscle and subcutaneous tissue by MR scanning; body composition analysis by H2 18O dilution, and hydrostatic weighing; and total and free T, dihydrotestosterone LH, FSH and SHBG. These studies should help dispel some of the myths surrounding the use of androgenic steroids.